The present invention relates to a method for manufacturing an aluminum alloy, and more particularly relates to such a method for manufacturing an aluminum alloy through the use of a reduction type reaction.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending U.S. patent application Ser. Nos. 820,886 and 888,650, which may be considered to be material to the examination of the present patent application.
In the prior art, there have been proposed various types of method for manufacturing an aluminum alloy. In particular, in Japanese Patent Application Laying Open Publication Serial No. 59-256336 (1984), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed a method for manufacturing an alloy of a first base metal which for example may be aluminum and a second additive metal which has a weaker affinity for oxygen than said first base metal (but may have a much higher melting point than said first base metal), in which a porous block like preform is made of an oxide of the second additive metal, and then a quantity of the first base metal in molten form is permeated through the interstices of this porous preform, so as to come into intimate contact with the material thereof which is the oxide of the second additive metal. As this occurs, said molten first base metal reduces this oxide of said second metal, due to the fact that said first metal has a greater affinity for oxygen, i.e. has a greater oxide formation tendency, than does said second metal. Accordingly, said oxide of said second additive metal is, hopefully, all reduced, so as to leave said second additive metal in alloyed form with said first base metal, while of course producing a certain quantity of the oxide of said first base metal which need not present any problem. And a distinguished advantage of this alloying process is that it is not necessary to raise the working temperature so high as to melt said second additive metal, which may be a very high melting point metal such as nickel or titanium or the like, but it is on the contrary only necessary to melt the first base metal which may be a relatively low melting point metal such as aluminum or aluminum alloy. And in the case of this alloying method there are no substantial limitations on the type or the quantity of the second additive metal which is to be alloyed to the first base metal, and it is thus possible to manufacture an alloy of any desired composition, as opposed to the case of a conventional type of allowing process in which there are various inevitable restrictions due to reasons including but not limited to rise in the dissolution temperature of the alloy or of its materials, degradation of alloying characteristics, and differences in the specific gravities of the materials to be alloyed. Further, in the case of the above outlined alloying method it is possible to regulate a specific part of a cast object to be of substantially any desired composition.
In the case of the above outlined alloying method, in the case that the first base metal is aluminum or an alloy thereof, the reduction of the second additive metal is brought about by means of a thermite reaction that occurs between the molten aluminum or aluminum alloy base metal and the oxide or oxides of the porous perform including the second additive metal. This enables the manufacture of aluminum alloys that may be of substantially any desired composition, and whose composition may be locally varied as desired.
However, there is a disadvantage with the above outlined alloying method in its form as described above, as follows. If a conventionally available aluminum alloy is selected as the first base metal to be alloyed, as is per se desirable on the grounds of cost and convenience, there are many cases in which a satisfactory thermite reaction is not produced, and there is in practice no assurance that a satisfactory alloying process will occur and that the first base metal and the second additive metal will be properly alloyed together and will be properly commingled. In detail, if substantially pure aluminum is used as the first base, metal, than no substantial problem tends to arise: thus, if pressurized infiltration of molten substantially pure aluminum alloy into a high porosity block formed of powdered oxide of another metal, such as Fe.sub.2 O.sub.3, NiO, or MnO, which has a particle diameter of less than one micron, is conducted, then indeed a sufficiently effective thermite reaction occurs, and the powdered oxide of said other metal is indeed satisfactorily reduced, so as to produce a quantity of aluminum oxide which presents no substantial problem, and so as to release a quantity of said other metal, such as Fe, Ni, or Mn, into the aluminum alloy to be alloyed therewith. Thereby, the desired high quality alloy, such as an Al-Fe alloy, and Al-Ni alloy, or an Al-Mn alloy, can be satisfactorily produced. However, in the more common case that it is desired to utilized as the material for being infiltrated in said high porosity preform an alloy of aluminum containing a substantial amount of silicon, such as aluminum alloy of type JIS standard AC8b 8A, then there is a tendency for the silicon in the molten aluminum alloy mixture to crystallize out on the surfaces of the small particles of the oxide of the additive metal that make up the preform, and this can impede the thermite reaction between the aluminum alloy and said small oxide particles, and can result in the incomplete reduction of said oxide of said second additive metal. Experimental results verifying this phenomenon are presented later in the specification under the title of "Background Experiments". This can present a serious problem in circumstances of actual industrial application.